This application claims the priority of Austrian Patent Application Serial No. A 1869/2000, filed Nov. 3, 2000, the subject matter of which is incorporated herein by reference.
The present invention relates to an apparatus for producing a stranded cable with alternating twist directions (SZ-stranding), and more particularly to a apparatus that is capable of driving storage disks located between an entrance guide and a stranding disk at different rotation speeds.
Unlike stranding methods using a uniform twist direction, alternating or SZ-stranding, wherein the twist direction of the strand elements changes after a certain length, does not require rotating baskets for the strand elements. These rotating spools typically permit only production of a limited length for the cable, whereas SZ-stranding allows continuous production at high drawing speeds. The strand elements traverse a stranding section that is generally bound by a fixed entrance guide and a stranding disk that can be rotated in alternating directions. To prevent the strand elements from becoming entangled within the stranding section, holding elements and/or storage disks are typically disposed between the entrance guide and the stranding disk which have through holes for guiding the strand elements. The invention is directed to driving of those storage disks.
Apparatuses are known from EP 0 932 165 A1 and EP 0 767 965 B1 wherein the storage disks are driven via a connection having rotational elasticity. For this purpose, a torsion element is used that is affixed in the region of the entrance guide and is driven in alternating directions in the region of the stranding disk. In EP 0 932 165 A1, the stranding disk and the storage disks are secured directly on the torsion element against rotation, whereas the torsion element in EP 0 767 965 B1 is spaced-apart from and parallel to the rotational axis of the stranding disk and the storage disks. The stranding disk and/or the storage disks are driven by transmission elements which are affixed on the torsion element and engage with the stranding disk and/or the storage disks. In both embodiments, the storage disks are driven at different rotations speeds that decrease with increasing distance from the stranding disk. This arrangement effectively prevents the strand elements in the stranding section from becoming entangled.
The aforedescribed embodiments, however, have in common that it is difficult to adjust the rotation speed of the individual storage disks with the required accuracy. Accordingly, an attempt was made to accurately control the local rotation speed by varying the elastic modulus of the torsion elements over the running length. This approach is no longer feasible at the greater rotation speeds common with SZ-stranding due to the increasingly significant mass inertia within the torsion elements. Individual storage disks can retain their previous rotation direction during a short time when the rotation direction of the drive in the region of the stranding disk is reversed. This causes an undesirable and uncontrolled phase shift of the storage disks which places an upper limit on the achievable stranding speed.
It would therefore be desirable to provide a stranding apparatus with a torsion element that drives the storage disks and simultaneously allows a precise control of the rotation speeds of the individual storage disks.
According to one aspect of the invention, an apparatus for manufacturing a stranded cable from strand elements with alternating twist directions (SZ stranding) is provided, which includes a guide adapted to receive the strand elements and a stranding disk that can be driven in alternating directions. The apparatus further includes a plurality of storage disks disposed between the guide and the stranding disk. At least one torsion element is provided that is driven at several locations along the torsion element with different rotation speeds, with the storage disks being driven in such a way that their rotation speed decreases with increasing distance from the stranding disk.
With this arrangement, the required driving torque can be applied to the torsion elements at different locations. Only very small corrections to the torque are required when using a single torsion element which thereby operates as a transmission gear for the individual storage elements. Most importantly, these additional torque corrections substantially eliminate the disadvantages associated with a single drive for the stranding disk, thereby permitting greater stranding speeds.
According to an advantageous embodiment of the invention, stranding machines that have to produce large stranding forces for manufacturing a stranded product may include individual drive units located at at least two locations of the torsion element. Conversely, lightweight stranded products may be produced using only a single main drive having a gear with driving several driven assemblies that are non-rotatably connected with the torsion elements.
When a flexible design is desired that allows an easy exchange of the torsion element, the torsion element may be located spaced apart from and parallel to the longitudinal axis of the stranding section. The storage disks can be driven using transmission elements.
If a compact construction is desired, the torsion element can be guided centrally along the longitudinal axis of the stranding section, in which case the storage disks are non-rotatably secured directly on the torsion element and drive the torsion element directly. This obviates the need for separate drive disks in addition to the already existing storage disks.
A better control over the rotation speed of the individual storage disks can be achieved by varying the elastic modulus of the torsion element over its length.
According to another advantageous embodiment of the invention, the torsion element can be made of at least two, preferably four, mutually parallel individual rods, whereby the tendency of the torsion element to oscillate in the transverse direction is significantly reduced.